A number of existing medical treatments involve percutaneously inserting or implanting objects in a patient. One such treatment is brachytherapy for prostate cancer. In brachytherapy, radioactive sources or “seeds” are implanted relative to a tumor to provide a high dose of radiation to the tumor but not the surrounding healthy tissue. Other oncological treatments involve percutaneously implanting radio-opaque markers or signal-generating markers adjacent to the tumor. The markers identify the location of the tumor so that a high dose of radiation from a linear accelerator or other external source can be focused directly at the tumor.
FIGS. 1A and 1B are cross-sectional views of a two-piece introducer 100 of the prior art. Referring first to FIG. 1A, the introducer 100 includes a needle 102 and a stylet 104 slidably disposed within the needle 102. The stylet 104 includes a first handle 101 and a blunt distal end 106. The needle 102 includes a second handle 103 and a cannula 108 extending through the second handle 103. The cannula 108 is configured to hold radioactive seeds 110 or other objects. The cannula 108 has a distal tip 105 configured to percutaneously penetrate the patient for implantation of the seeds 110 in the patient. Inert spacers 111 can be used to provide the desired spacing between the seeds 110 when the seeds 110 are implanted in the patient. The seeds 110 and spacers 111 are retained in the cannula 108 by a plug 112 made from bone wax or other suitable bio-compatible materials.
To implant the seeds 110 at a target location in a patient (not shown) in the desired pattern as loaded in the cannula 108, an operator (also not shown) pushes the cannula 108 in a first direction 120 to insert the tip 105 into the patient. The operator then pushes the second handle 103 further in the first direction 120 to position the tip 105 at the desired depth within the patient where the seeds 110 are to be released. Throughout this motion, the operator moves the needle 102 and the stylet 104 together as a unit. At the desired depth, the operator grasps the first handle 101 with one hand and the second handle 103 with the other hand and, while holding the first handle 101 stationary, slides the second handle 103 back in a second direction 122 toward the first handle 101. As shown in FIG. 1B, this movement causes the cannula 108 to pull back from the plug 112, the seeds 110, and the spacers 111 to implant them in the patient.
One shortcoming of the prior art introducer 100 is that the two-handed movement required to properly release the seeds 110 at the target location and in the desired pattern may be somewhat awkward and nonintuitive. As a result, the operator is prone to err and may inadvertently misplace the seeds 110. For example, to properly release the seeds 110, the operator must hold the first handle 101 stationary while sliding the second handle 103 back in the second direction 122 toward the first handle 101. If, instead, the operator accidentally pushes the first handle 101 toward the second handle 103, then the stylet 104 may push the seeds 110 out of the cannula 108 in the first direction 120. This movement could cause the seeds 110 and the spacers 111 to collide in a “train wreck” just beyond the tip 105 of the cannula 108. Either way, the seeds will not be positioned accurately relative to the target location or in the desired pattern. A further shortcoming of the prior art introducer 100 is that the bone wax used for the plug 112 in brachytherapy applications may melt prematurely allowing the seeds 110 to migrate out of the cannula 108 before reaching the desired target location. As such, conventional introducers for brachytherapy applications are custom loaded at the treatment facility and are not suitable for being transported in warm environments.